Pulso de oxigêncio: da fisiologia ao valor prognóstico em indivíduos saudáveis e com doenças cardiovasculares

Abstract

In the present doctored dissertation, we attempted to elucidate some aspects related to the prognostic value of maximum oxygen pulse (O2p) and the pattern of its curve during progressive exercise. In this sense, three independent and original studies were developed. In the first study, the ability of maximal O2p and maximal oxygen uptake (VO2max) to predict mortality was investigated in patients with and without cardiopulmonary disease. Over a mean follow-up of 6.3± 3.2 years, there were 126 deaths out of 948 patients tested. The relative risks of mortality was nearly 3-fold higher (HR 2.73 IC a 95% 1.73 a 4.32) among participants with both maximum O2p and VO2max responses below normal cut-points (VO2max < 16 mL.kg-1.min-1 e O2p < 12 mL.beat-1) compared with participants with both responses above the normal cut-points. The mortality rates in 10 years of follow-up was also significantly reduced in those with both responses abnormal (59% vs. 88%; p <0.05). In the second study, the ability of VO2max and maximum O2p pulse to predict cardiac events was examined in a cohort of 998 heart failure patients. There were 212 cardiac events (176 deaths) over a mean of 28 ± 26 months of follow-up. Patients exhibiting abnormalities for both responses (VO2max < 14.3 mL.kg-1.min-1 and maximum relative O2p <85% of age-predicted) had 4.8-fold (95% confidence interval 2.7 to 8.5) higher risk for mortality than those whose responses were normal. More important, age-predicted maximum O2p also predicted mortality in patients in the intermediate range of VO2max (10 to 14 mL.kg-1.min-1). The 3-year mortality rate for patients in this range who had age-predicted maximum O2p values <85% was even slightly higher than those with VO2max &#8804;10 mL.kg-1.min-1 (57% vs. 60%, respectively). In the third study, after testing the prognostic value of maximum O2p, we decided to evaluate the O2p curve pattern response to incremental exercise in 100 subjects re-tested under similar clinical conditions and testing protocol. To analyze the O2p curve pattern, the sample was divided into quintiles of maximum relative O2p and the slopes and intercepts of the O2p curves compared among CPX. After excluding the first minute of CPX (rest-exercise transition), the relative O2 pulse curve showed a linear increase, as demonstrated by the high coefficients of determination (R2 from 0.75 to 0.90; p<0.05 for all quintiles). Even though maximum oxygen uptake and relative O2 pulse were significantly higher in the second CPX for each quintile of relative O2 pulse (p<0.05 for all comparisons), no differences were found when slopes and intercepts were compared between the first and second CPXs (p>0.05 for all comparisons; except for intercept in the 5th quintile). the relative O2 pulse demonstrated a stable linear increase throughout maximum exercise in adults retested under same clinical conditions